great meal in Santorini?

We're looking forward to a few great days in Santorini in April, and we are thinking of having one very nice dinner. We were thinking of Selene, but have also received suggestions for places likes Vanilla, Ambrosia and 1800. Are any of these appropriate (or more appropriate) if we are traveling with a well-behaved elementary school-aged child? Are places open for dinner at 8:30 or 9?

I can't comment too much on the places you mentioned. We had made a reservation for Ambrosia but ended up canceling just because we wanted to play things more by ear that evening. From what I recall, Ambrosia is a teeny, tiny place and very intimate...more for couples. 1800 seemed bigger, but it bit more formal in a more old-fashioned (nice) sort of way. Selene looks lovely from the website but we didn't see it while we were in Santorini.

For other less formal places, we had some good meals at Roka and Kyprida. We even went to Kyprida twice.

Places are most definitely open for dinner at 8:30 and 9. In fact, those with good views of the sunset get quite busy right at dusk as people stake out their spots for a good view. It's quite amusing actually. When we were there, sunset was at about 7-7:30.